middle::cfg code cleanup.

Namely:

 1. Now that cfg mod is used for dataflow, we do not need to turn on
    the `allow(deadcode)` to placate the linter.

 2. remove dead struct defn.

src/librustc/middle/cfg/mod.rs

@@ -15,8 +15,6 @@ Uses `Graph` as the underlying representation.
 
 */
 
-#![allow(dead_code)] // still a WIP, #6298
-
 use middle::graph;
 use middle::ty;
 use syntax::ast;
@@ -48,11 +46,6 @@ pub type CFGNode = graph::Node<CFGNodeData>;
 
 pub type CFGEdge = graph::Edge<CFGEdgeData>;
 
-pub struct CFGIndices {
-    entry: CFGIndex,
-    exit: CFGIndex,
-}
-
 impl CFG {
     pub fn new(tcx: &ty::ctxt,
                blk: &ast::Block) -> CFG {